This invention relates generally to device for reading-out a two-dimensional charge image, and more particularly, to a device wherein such reading-out is achieved by means of an array which contains stacked circuit boards. One of the flat sides of each circuit board is provided with recesses which extend parallel to the narrow sides of the circuit boards, and which contain electronic components. The invention further relates to device wherein control lines for the electronic components are arranged on a flat side of the circuit board, and wherein one of the narrow sides of each circuit board is provided with electrodes; the electrodes of the circuit boards being ordered as a matrix in rows and columns.
Device for reading-out a two-dimensional ultrasonic image is known to be provided for an ultrasonic camera. Such known device contains a stack of several, illustratively sixteen, one-dimensional arrays. Each such array has several elementary converters and a multiplexer, and optionally also an amplifier and a filter. The electronic circuitry is arranged in a slot of a circuit board which is preferably a ceramic plate, and which forms this linear array. The depth of one of the one-dimensional arrays is illustratively 1.5 mm. The known apparatus is described in "IEEE Ultrasonics Symposium", 1980, pages 766 to 769.
In the known device, the connecting lines between the inputs of the multiplexer and the elementary converters of each one-dimensional array have different lengths. The number of elementary converters on the end face of one of the circuit boards is limited, as determined by the multiplexer inputs. The number of converters may be, for example, 16 or 32, or an integral multiple of these multiplexer inputs.
In a further known device for reading-out a two-dimensional ultrasonic image by means of an integrated acoustic array, a two-dimensional array is provided with a matrix of dual-gate MOS-FETs ordered in rows and columns. In known integrated circuit technology, for example, 8 dual-gate MOS-FETs in each row and in each column can be provided for a total of 64 such dual-gate MOS-FETs. The dual-gate MOS-FETs are known to persons skilled in the art as "MOS-FET tetrodes." Every element of the matrix consists of a gate leak resistor, an elementary converter, and a dual-gate MOS-FET, wherein the gate leak resistor and the elementary converter are electrically connected in parallel and to the first gate terminal of the dual-gate MOS-FET. The second gate of each dual-gate MOS-FET of each column is connected to an address line, and each drain terminal of the dual-gate MOS-FET of a row is connected to a read line. This arrangement is described in "Integrated Acoustic Array and Acoustical Holography", volume 7, Kessler (Editor), Plenum Press, pages 423 to 455.
In this known device, the currents in a line within the matrix can combine additively, such that in the case of a large matrix such added currents can produce an overload at the signal line, or also may lead to excessively large voltage drops along this line.
It is, therefore, an object of this invention to improve the known devices. More particularly, it is an object of this invention to select the number of electrodes of each row continuously and without being required to be an integral multiple of the inputs of electronic modules.
it is a further object of this invention to provide an arrangement wherein all connecting conductors from the elementary converters to the inputs of the corresponding switchable amplifiers are of at least approximately equal length.